Wash. Rev. Code § 24.06.015
Corporations may be organized under this chapter for any lawful purpose including but not limited to mutual, social, cooperative, fraternal, beneficial, service, labor organization, and other purposes; but excluding purposes which by law are restricted to corporations organized under other statutes.
[ 1969 ex.s. c 120 s 3.]
Labor unions: Chapter 49.36 RCW.